1. Field of the Invention
The present invention relates generally to magnetic heads for reading data written to storage media, and more particularly to magnetic read heads for disk drives.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” onto which the read/write sensors of the magnetic head are fabricated. The slider flies above the surface of the disks on a thin cushion of air, and the surface of the slider which faces the disks is called an Air Bearing Surface (ABS).
The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads has become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
Some recent read heads use a tunnel junction sensor, also known as a “tunnel valve”, abbreviated “TV”, for reading the magnetic field signals from the rotating magnetic data storage disk. The sensor typically includes a nonmagnetic tunneling barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. The pinned layer in turn is fabricated on an antiferromagnetic (AFM) pinning layer which fixes the magnetic moment of the pinned layer at an angle of 90 degrees to the air bearing surface (ABS). The magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from the rotating magnetic disk. The tunnel junction sensor layers are typically sandwiched between ferromagnetic first and second magnetic shield layers. These first and second shield layers also serve as first and second electrical lead layers, and are connected to the tunnel junction sensor for conducting a tunneling current through it. The tunneling current is preferably configured to conduct Current Perpendicular to the Planes (CPP) of the film layers of the sensor, as opposed to a sensor where a sense Current In the Planes (CIP) or parallel to film layers of the spin valve sensor. The CPP configuration is attracting more attention lately, as it can be made to be more sensitive than the CIP configuration, and thus is more useful in higher densities of tracks and data. The sensitivity of the tunnel junction sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the tunnel junction sensor from minimum resistance to maximum resistance and R is the resistance of the tunnel junction sensor at minimum resistance.
The track width and the stripe height refer to the width of the read head sensor stack and the length dimension perpendicular to the ABS. Both of these dimensions are very important to the operating characteristics of the read head and are very tightly controlled during fabrication. The trackwidth and stripe height of magnetic tunnel junctions and CPP-GMR read sensors are defined usually by ion milling. This ion milling creates redeposited material on the side of the barrier layer, which can cause unwanted barrier layer shorting.
FIG. 5 (prior art) shows a wafer stack 52 of thin film layers which is being shaped into a CPP read head sensor in a front plan view as seen from the Air Bearing Surface (ABS). The stack 52 includes a first magnetic shield 54. A first seed layer 58 is deposited upon the first magnetic shield 54. Further layers are formed in the order of an antiferromagnetic layer 60, a pinned layer 62, a barrier layer 64, a free magnetic layer 66, and a cap layer 68. It can be seen that a bridge of unwanted redeposited material 70 has been formed across the barrier layer 64, thus creating a “short” between the pinned layer 62 and the free magnetic layer 66, which can severely affect the operation of the sensor.
A shallow angle ion milling step can be conducted to remove this redeposited material. However, excessive ion milling of the sensor edge causes sensor damage, thus reducing output signal amplitude. The amount of redeposited material is higher in the case of the sharp junction profiles created when a non-undercut mask layer is used for ion milling.
Thus there is a need for a method of fabrication which eliminates creation of bridges of unwanted redeposited material which causes shorting across the barrier layer when ion milling is used to shape sensor material stacks.